diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 87f4fd6..5b28ced 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -38,4 +38,7 @@ jobs:
 
       - run: opam exec -- dune build -p mlx,ocamlmerlin-mlx
 
+        # TODO: pass --with-dev-setup to opam instead? (requires opam 2.2, I think)
+      - run: opam install menhir.20210419 menhirLib.20210419 menhirSdk.20210419
+
       - run: opam exec -- dune runtest